(22b) Sterile Filtration of mRNA-Lipid Nanoparticle Vaccines – New Challenges for an Old Technology

The use of microfiltration membranes to remove bacteria from various process streams dates back more than 100 years to the early work by Zsigmondy. Although sterile filtration of monoclonal antibodies and other recombinant proteins is relatively straightforward, the situation is dramatically different with viral and mRNA-lipid nanoparticle vaccines, like those used for protection against Covid-19. These vaccines have particles that are 100 – 400 nm in diameter, which overlaps with the 0.2 µm rated pore size of today’s sterile filters. This causes extensive fouling, reducing the capacity and product yield while increasing the overall cost of manufacturing. This talk will examine recent efforts to develop effective sterile filtration steps for an mRNA lipid nanoparticle vaccine (LNP - produced by Moderna) using commercial sterile filters. Sterile filtration of the LNP showed a significant increase in capacity at high pressures with the fouling deposit providing less resistance to flow, which is exactly opposite to the behavior expected for a compressible foulant. The flux decline behavior was analyzed using classical blocking filtration laws, with the results consistent with the complete pore blockage model. The mRNA-LNP deposit formed on the surface of sterile filtration membranes using a combination of electron microscopy imaging, atomic force microscopy, and hydraulic resistance measurements. The reduction in resistance at high pressures is due to intrusion of the mRNA-LNP deposit through the membrane pores. Taken together, these results provide important insights into the physical properties of the fouling deposit and its impact on the sterile filtration of LNP used in the production of these important biotherapeutic products.